uAbstract

uAbbreviated figure captions

uFault study

u3D reflection data

u2D reflection data

uFault zone structure

uShallow stratigraphy

uResults

uAcknowledgments

uComplete figure captions

uAbstract

uAbbreviated figure captions

uFault study

u3D reflection data

u2D reflection data

uFault zone structure

uShallow stratigraphy

uResults

uAcknowledgments

uComplete figure captions

uAbstract

uAbbreviated figure captions

uFault study

u3D reflection data

u2D reflection data

uFault zone structure

uShallow stratigraphy

uResults

uAcknowledgments

uComplete figure captions

uAbstract

uAbbreviated figure captions

uFault study

u3D reflection data

u2D reflection data

uFault zone structure

uShallow stratigraphy

uResults

uAcknowledgments

uComplete figure captions

uAbstract

uAbbreviated figure captions

uFault study

u3D reflection data

u2D reflection data

uFault zone structure

uShallow stratigraphy

uResults

uAcknowledgments

uComplete figure captions

uAbstract

uAbbreviated figure captions

uFault study

u3D reflection data

u2D reflection data

uFault zone structure

uShallow stratigraphy

uResults

uAcknowledgments

uComplete figure captions

uAbstract

uAbbreviated figure captions

uFault study

u3D reflection data

u2D reflection data

uFault zone structure

uShallow stratigraphy

uResults

uAcknowledgments

uComplete figure captions

Abbreviated Figure Captions

(Complete captions accompany full-size images and follow text.)

Figure 1. Index map. The box on the inset map shows the location of the Palos Verdes fault and study area. The polygon shows the area of the 3D seismic data. Lines in violet show the 2D seismic profile locations. Mapped faults are in red.

Figure 2. Chair-cut visualization of Beta oil field 3D survey, cut at line 120, CDP 650, and time 1800 ms. Positive amplitudes are in red; negative amplitudes, in blue.

Figure 3. A fence diagram of the locations of three 2D lines on top of the 1436-1492 ms 3D time-slice. Green vertical lines show well locations with log data.

Figure 4(a-c). Beta 3D data time slices. (a) 168 ms, (b) 588 ms, and (c) 1468 ms. Green lines show intersection of high resolution 2D seismic lines with 3D time slice. The main trace of the Palos Verdes fault is shown in brown.

Click here to view sequence of Figure4(a), (b), and (c).

Figure 5. The location of the segments and features of the Palos Verdes fault through the Beta 3D survey area.

Figure 6(a-e). Individual cross-sections through segments A through E are labeled A-A’ through E-E’ and shown with interpreted faults and horizons.

Click here to view sequence of Figure 6(a), (b), (c), (d), and (e).

Figure 7. A broad anticline, perpendicular to the fault, below Pliocene horizon “C-2.”

Figure 8(a-b). Close-ups of 300 ms of 2D data from (a) line 80a, above, and (b) 81, below, have been annotated to show approximate location of the Quaternary wedge of sediments overlying anticlinoria, fault zone, and graben.

Figure 9. 2-D, E-W seismic line 81 that extends across and beyond the study area. The Palos Verdes fault zone (PVF) is characterized by change in character across it, as well as the development of the Quaternary wedge highlighted in Figure 8(b).

Why Study the Fault?

• Does the Palos Verde fault (Figure 1) pose a hazard to the Los Angeles area?

• What is the present sense of motion, if any, along the fault?

• Has this motion changed over time?

• How effective is it to combine petroleum industry 3D with high-resolution 2D data to interpret structure and geometry?

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3D Seismic Reflection Data (Figure 2)

• Acquired for petroleum exploration

• 392 lines at 54 m spacing

• 671 cross lines at 25 m spacing

• 4 ms voxel depth

• 3 s two-way travel time

2D Seismic Reflection Data (Figure 3)

• Acquired by California State University, Long Beach (CSULB)

• 4 kJ sparker source

• 16 channels

• 6.25 m shot spacing

• 3.125 m CDP spacing

• 0.25 ms sample interval

• 0.95 s two-way travel time

Seismic Processing Steps

• Verify header data, quality control data.

• Correct spherical divergence, remove noise spikes, normalize trace amplitudes.

• Deconvolve and filter.

• Set geometry correction parameters.

• Common reflection point gather.

• Velocity analysis, normal move-out correction, stack, predictive deconvolution.

• Post-stack migration.

Fault Zone Structure

The Palos Verdes fault zone has a general northwest trend (Figures 1 and 2). Bends in the fault are associated with bathymetric changes; similarly, there are topographic changes along the Newport-Inglewood  and Whittier faults, the other two major right-slip faults of the Los Angeles Basin.. The fault zone with its pop-up structure includes multiple fault strands. It separates the study area into two distinct seismic characters--Palos Verde anticlinorium to the west and Wilmington “graben” to the east (Figures 1, 2, and 3).

Time slices reveal a releasing bend in the southern part of the study area and a restraining bend in the center of the study area (Figures 4 and 5). The fault trend is near vertical to at least 3 s.

Anticlines within the study area are the San Pedro Bay anticlinorium and the “Beta ear” anticline west of the fault (Figure 6). Also west of the fault are the toe of the Palos Verdes Hills anticlinorium (in the north) and the underlying basement ridge. East of the fault is the Wilmington “graben,” with the THUMBS –Huntington Beach fault at the northeast edge of the study area and the main Beta oilfield monocline along the restraining segment of the Palos Verdes fault. A broad anticline, perpendicular to the fault, with associated growth during the Pliocene, may indicate the initiation of right-slip motion along the fault zone (Figure 7).

Detailed Shallow Stratigraphy

The narrow, tilted wedge of Quaternary strata southwest of the fault is generally too shallow to be effectively imaged with the 3D data. However, lines from 2D seismic data show the approximate location of the Quaternary wedge of sediments overlying the Palos Verdes Hills and San Pedro Bay anticlinoria, the Palos Verdes fault zone, and the Wilmington “graben” (Figures 8 and 9). This growth wedge and the monocline east of the fault are variable along strike; they may reflect uplift that formed as sediments were translated into the restraining bend.

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Results

• The combination of 2D and 3D is more effective for offshore fault zone investigations than 2D or 3D alone.

• There are 5 geometrically distinct segments of the Palos Verdes fault in the San Pedro Bay study area.

• Each of these faults segments is near vertical to at least 3 s two-way travel time.

• Each segment has 1-5 major strands that disrupt the most recent sediments and are expressed in bathymetry.

• Segments include restraining and releasing geometry.

• Recent basin inversion is from sediments translating from a releasing bend into a restraining bend.

• The fault is primarily right-lateral strike-slip and has been since at least mid-Pliocene.

Acknowledgments

3D data provided by Chevron-Texaco.

Research funded by Southern California Earthquake Center.

Complete Figure Captions

Figure 1. Index map. The box on the inset map shows the location of the Palos Verdes fault and study area. The polygon shows the area of the 3D seismic data. Lines in violet show the 2D seismic profile locations. Mapped faults are in red. Note changes in bathymetry associated with bends in the Palos Verde fault (PVFZ). Similarly, the topography changes along the Newport-Inglewood ((NIFZ) and Whittier (WF) faults, the other two major right-slip faults of the Los Angeles Basin (LA Basin).

Figure 2. Chair-cut visualization of Beta oil field 3D survey, cut at line 120, CDP 650, and time 1800 ms. Positive amplitudes are in red; negative amplitudes, in blue. The general northwest trend of the fault zone with its pop-up structure is visible and separates the volume into two distinct seismic characters with Palos Verde anticlinorium to the west and Wilmington “graben” to the east. Note the complex structure of the fault zone, which includes multiple fault strands. Additionally, several Pliocene to Quaternary horizons have been added.

Figure 3. A fence diagram of the locations of three 2D lines on top of the 1436-1492 ms 3D time-slice. Green vertical lines show well locations with log data. Palos Verdes fault location is superimposed with the orange wireframe, and acoustic basement is shown as a surface when color changes with depth.

Figure 4(a-c). Beta 3D seismic time slices. (a) 188 ms, (b) 368 ms, and (c) 1468 ms. Green lines show intersection of high resolution 2D seismic lines with 3D time slice. The main trace of the Palos Verdes fault is shown in brown. Time slices reveal a releasing bend in the south of the study area and a restraining bend in the center of the study area. Although more difficult to see through multiples and poorer quality 3D above about 400 ms and below the basement contact, the fault trend is near vertical to at least 3 s.

Figure 5. The location of the segments and features of the Palos Verdes fault through the Beta 3D survey area. Green lines indicate the locations of the three 16-channel seismic lines; background is a time slice of the 3D survey at 1200 ms.

Figure 6(a-e). Individual cross-sections through segments A through E are labeled A-A’ through E-E’ and shown with interpreted faults and horizons. Anticlines within this survey are the San Pedro Bay anticlinorium (SPBA) and the “Beta ear” anticline to the west of the fault. Additionally to the west of the fault is the toe of the Palos Verdes Hills anticlinorium (PVHA) in the north and the underlying basement ridge. The latter is most likely a remnant Miocene bathymetric high at the peak of a tilted crustal block due to Borderland extension and rotation. To the east of the fault is the Wilmington “graben” with the THUMBS –Huntington Beach fault at the northeast edge of the survey and the main Beta oilfield monocline along the restraining segment (c) of the Palos Verdes fault.

Figure 7. A broad anticline, perpendicular to the fault, below Pliocene horizon “C-2,” with associated growth through “C-top,” may be an indicator of initiation of right-slip motion along the fault zone. Color indicates depth to horizon “C-2.”

Figure 8(a-b). Close-ups of 300 ms of 2D data from (a) line 80a, above, and (b) 81, below, have been annotated to show approximate location of the Quaternary wedge of sediments overlying the Palos Verdes Hills and San Pedro Bay anticlinoria (unconformity in green), the Palos Verdes fault zone (PVF), and the Wilmington “graben.” The narrow tilted wedge of Quaternary strata lying to the southwest of the fault is generally too shallow to be effectively imaged with the 3D data; note line 80a roughly corresponds to cross-section D-D’ (Figure 6(d)). This growth wedge and the monocline to the east of the fault appear variable along strike and may be due to uplift created as sediments have been recently translated into the restraining bend.

Figure 9. 2-D, E-W seismic line 81 that extends across and beyond the study area. The Palos Verdes fault zone (PVF) is characterized by change in character across it, as well as the development of the Quaternary wedge highlighted in Figure 8(b).

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